Injectable pharmaceutical formulations are well known in the art. See Remington's Pharmaceutical Sciences, Mack Publishing Company, Easton, PA, 16th Edition, 1980. Usually such formulations are in the form of dispersions such as colloids, emulsions and suspensions. More recently, sustained release injectable formulations comprising polymers have been used.
Typical sustained release injectable formulations include aqueous or water-miscible suspensions, but such suspensions often present stability problems and may not provide long enough retention time of the active in the formulation, either because the dispersion breaks down or because the dispersion is too soluble in the surrounding body fluids (e.g., the blood and lymph systems).
An example of a successful aqueous-based sustained release suspension is the protamine-zinc-insulin suspension. The United States Pharmacopeia (USP) entry for the suspension indicates a standard formulation as containing 40-100 USP Insulin Units/ml of an aqueous solution of zinc (0.15 to 0.25 mg zinc/100 USP Insulin Units) and protamine (1 to 1.5 mg protamine/100 USP Insulin Units) at pH 7.1 to 7.4. Typically the pH is maintained by 0.15 to 0.25% (w/v) dibasic sodium phosphate and the formulation also contains 1.4 to 1.8% (w/v) glycerin and 0.18 to 0.22% (w/v) cresol or 0.22 to 0.28% (w/v) phenol. Depending on the insulin concentration and the response of the patient, one injection releases insulin for up to three days.
Interferons are a family of proteins which exhibit antiviral activity against certain viruses and anticancer activity against certain cancers. Interferons include natural or recombinant alpha (leucocyte), beta (fibroblast) and gamma (immune) interferon, but alpha interferons are preferred for use in the compositions of this invention. Human alpha interferon is a naturally occurring mixture of at least eleven components including those designated alpha.sub.1 and alpha.sub.2 interferon, the latter being more preferred in this invention. Human alpha interferon exhibiting biological properties similar to naturally occurring alpha interferon can be made by recombinant methods. Rubenstein, Biochem. Biophys. Acta., 695, 5-16 (1982); Nagata et al., Nature, 284, 316320 (1980); EP 32,134; and U.S. Pat. No. 4,289,690 disclose methods for preparing alpha.sub.2 interferon. Also included within the scope of this invention are the so-called alpha hydrid interferons wherein fragments of two or more native alpha interferon species are joined (See, for example, EP No. 51,873). Parenteral administration of alpha.sub.2 interferon has been reported to be effective in the treatment of Kaposi's sarcoma, basal cell carcinoma, multiple myeloma and viral warts. The effective dose of alpha interferon can be easily determined by those skilled in the art.